Problem: $-\dfrac{7}{10} + \dfrac{1}{3} = {?}$
$ = - {\dfrac{7 \times 3}{10 \times 3}} + {\dfrac{1 \times 10}{3 \times 10}} $ $ = - {\dfrac{21}{30}} + {\dfrac{10}{30}} $ $ = - \dfrac{{21} + {10}}{30} $ $ = -\dfrac{11}{30}$